TELEREADER CWR-685E, Руководство по обслуживанию

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4.6 Trouble of RTTY
The speed of RTTY transmission and reception is selected by the BAUD six-position switch. Turn on
only one of the buttons. If two or more buttons are turned on or all buttons are turned off, the
system does not operate normally. When transmitting, do not change over this switch, but change
over the baud rate after returning to reception.
When the three-position switch for shift changeover is in OFF position in all buttons, 170 Hz shift is
selected.
When the HIGH, LOW switches are both in OFF position, a high tone is selected.
5. Description of MODEM printed circuit board performance
5.1 Demodulator
Signals at 30 mV to 2 Vpp fed from the AF IN terminal are evened out to about 3 Vpp by 1/4 IC3
and TR3. The Outputs can be checked at TP-1.
The evened signals are fed to 2/4 IC2 and passed through band pass filter of 800 Hz to 3,200 Hz,
and unnecessary Signal portions are taken out. Then the filtered signals are passed through a limi-
ter 1/4 IC3, and converted to signals stable in vertical direction. The signals can be checked on TP-
2.
Then necessary frequency should be selected by the programmable mark and space filters.
Remarks
VR-1 2295 Hz adj. High 170 shift
VR-2 2550 Hz adj. High 425 shift
VR-3 2975 Hz adj. High 850 shift
VR-4 1445 Hz adj. Low 170 shift
VR-5 2125 Hz adj. Low 425 shift
VR-6 1700 Hz adj. Low 850 shift
VR-7 2125 Hz adj. High tone mark
VR-8 1275 Hz adj. Low tone mark
VR 9
┐
They are for adjustment output
VR-10
┘
level, but are turned fully to
max. input at the time of
shipping.
* To obtain state with constant shift alone,
adjust so that TP-3 and TP-4 findings may
be identical.
The selected frequency can be checked on TP-3 and TP-4. Part of this output is amplified by the
LED amplifier, and is used to light up the LEDs of mark and space. Also signals for X, Y oscilloscope
of the monitor are taken out from this output.
The space and mark outputs become demodulation outputs by way of slicer, low pass filter, peak
detector, and comparator. The waveforms in this process are shown in the attached block diagram.